Along with the rapid development of communication technologies, expectations and requirements upon personal communications grow increasingly. Mobile network operators are required to pay special attention to factors such as user interface, quality of service, etc., which may directly impact user's experience on mobile services. Although 3rd Generation (3G) mobile communication system greatly attracts consumers with its broad bandwidth, varieties of services and high quality, there are still problems in 3G technologies restricting development of the mobile services. For example, how to fully utilize existing network resources after new network technologies are continually introduced, how to provide better service experience for users by combining the features and capabilities of different network technologies, etc. These unsettled problems restrict enlargement of market to some extent.
In a 3G network architecture defined by current standards, the mobile network is no longer limited to a Circuit Switched (CS) network, but gradually evolves into a Packet Switched (PS) network. From 3rd Generation Partnership Project (3GPP) Release 5, a core network of Universal Mobile Telecommunications System (UMTS) has been divided into three sub-systems, i.e., a CS domain, a PS domain and an IP Multimedia Subsystem (IMS).
The CS domain provides connections for CS services, and mainly includes the following functional entities: Mobile Switching Center (MSC), Gateway Mobile Switching Center (GMSC) and Inter-Working Function (IWF). The MSC provides switching and signaling control functions for the CS services. In an architecture with separated service control and bearer control, the MSC may include an MSC Server and a CS Media Gateway (CS-MGW). The GMSC provides routing and addressing functions for a mobile user in a network and may be co-located with the MSC or separated with the MSC. The IWF is closely related to the MSC and is used for interworking between a Public Land Mobile Network (PLMN) and an Integrated Service Digital Network (ISDN), or between the PLMN and a Public Switch Telecommunication Network (PSTN), or between the PLMN and a Public Data Network (PLMN). The primary function of the IWF is signaling conversion. The detailed function of the IWF may vary with different services and network types.
The PS domain provides connections for PS services, and mainly includes a General Packet Radio Service Support Node (GSN) used for packet transmission for PS service users. The GSN further includes a Serving GSN (SGSN) and a Gateway GSN (GGSN). The SGSN connects the core network and a Base Station Subsystem (BSS) or a Radio Network Controller (RNC), performs mobility management and session management of the PS services, and manages the mobility and communication services of a Mobile Station (MS) in the mobile network. The GGSN is an interface between the mobile communication network and another PDN. Meanwhile, the GGSN has a function of querying location information. Both the SGSN and the GGSN are able to provide charging information. In addition, a Boarder Gateway (BG) is configured at the edge of a GPRS network to interwork between two GPRS networks and ensure the security of the interworking.
Additionally, some functional entities are shared by the CS and PS domains, e.g. Home Location Register (HLR)/Authentication Center (AuC). The HLR manages subscription data and location information of the user, e.g., Mobile Station ISDN number (MSISDN), International Mobile User Identity (IMSI), subscribed Telephony services and supplementary services and application scopes of these services, MSC/VLR number, SGSN number, etc. The AuC stores authentication algorithms and security keys for users. Other functional entities include Visitor Location Register (VLR) which stores data of visited users, Equipment Identity Register (EIR) which stores International Mobile Equipment Identities (IMEI), Short Message Service (SMS) center gateway MSC, etc.
The IMS is a subsystem superposed on the existing PS domain in the Wideband Code Division Multiple Access (WCDMA) network in 3GPP R5. The IMS employs the PS domain as the bearer channel for the transmission of upper layer control signaling and media data, adopts Session Initial Protocol (SIP) as service control protocol, and provides abundant of multimedia services for users by separating the service control and the bearer control, and by utilizing the characteristics of the SIP, i.e., simple, extensible and convenient for media combination. The functional entities in the IMS mainly include: Call Session Control Function (CSCF), Application Server (AS), Home Subscriber Server (HSS), and Media Gateway Control Function/IMS Media Gateway (MGCF/IM-MGW). The CSCF is used for controlling user registration and session control. The AS is used for providing varieties of service logic control. The HSS is used for centralized administration of user's subscription data. And the MGCF/IM-MGW is used for interworking between the IMS and the CS network. The user accesses the IMS through a proxy node, Proxy-CSCF (P-CSCF), in an area where the user currently locates. A home domain service node in the area where the user registers, Serving-CSCF (S-CSCF), performs the session control, service triggering and the interaction with the AS. An Interrogating CSCF (I-CSCF) performs entrance query and topology hiding of the IMS. The HSS in the IMS is a superset of the HLR and functionally compatible with the HLR. In practical applications, the HSS and the HLR in the CS/PS domain are very likely to be two independent entities.
The IMS defined by the 3GPP standards solves critical problems concerning operability of multimedia services over IP, including roaming charging, Quality of Service (QoS), security, etc. The architecture and basic ideas of the IMS have been widely admitted in the industry. Both 3GPP2, which drafts the technical standards for cdma2000 system, and the TISPAN, which drafts the technical standards for the next generation of fixed network, define corresponding IP multimedia network architectures and service systems based on the IMS defined by the 3GPP, i.e., the IP multimedia systems defined by different organizations have the same architecture.
Meanwhile, the 3GPP has begun to study the Interworking of WLAN access with 3GPP system (I-WLAN), Fixed Broadband IMS access (FBI) and the all-IP network which supports multiple access technologies (AIPN). The user is able to access, based on his/her subscription, to the IMS via access networks of different access technologies with a single multi-mode terminal or different types of terminals so as to receive unified multimedia services including VoIP. Furthermore, in the 3GPP R7, a work item is approved to study the solution of Voice Call Continuity (VCC) between Circuit Switched (CS) and IP Multimedia Subsystem (IMS), within the work item, a requirement of routing selection between the CS domain and the IMS is raised when receiving an incoming call destined to a user to meet the demands of network and service developments.
In a new application environment with multiple available domains, in order to enrich the variety and diversity of services for the user and improve the mobile service market for the operators, the network is required to have an ability of selecting a domain via which a voice call is to be delivered. For example, deliver the voice call as the CS voice service via the GSM, WCDMA CS domain, cdma2000 CS domain or the PSTN, or deliver the voice call as the VoIP service via the IMS accessed via various fixed/mobile IPCAN. Then a new requirement of domain selection is brought out, i.e., when all incoming call destined to a user is received, how to select different domain to deliver the incoming call according to routing policy and other conditions. The settlement of the domain selection directly affects whether the user is able to register in multiple domains simultaneously and enjoy multi-domain voice service flexibly.
Because the requirement is originally raised in the 3GPP, the CS/IMS of the WCDMA system is mainly taken as an example hereinafter. But according to the foregoing descriptions, it can be seen that the requirement of domain selection also exists between CS voice services provided in the GSM, cdma 2000 CS domain and the PSTN and VoIP services provided in the IMS accessed via various fixed/mobile IPCAN.
To realize the domain selection in the CS/IMS, a Routing Policy Decision Point (RPDP) is introduced in the related art. During the domain selection procedure, the RPDP is queried for a routing decision. The RPDP makes the routing decision according to current routing policy pre-configured and stored in the PDCP and routing-decision-making related information of the user in the CS/IMS, determines routing information according to the routing decision, and returns routing information determined to a routing control entity in the CS/IMS which performs subsequent routing control for the incoming call according to the routing information.
The technical solution in the related art may have two implementation modes based on the type of an interface adopted for the query of the routing decision, i.e., a first mode adopting a call-control protocol based interface and a second mode adopting a non-call-control protocol based interface.
In the first mode, the routing control entity in the CS/IMS queries the RPDP for the routing decision through the call-control protocol based interface. For example, the GMSC in the GSM or in the WCDMA CS domain interacts with the RPDP functioning as a GSM Service Control Function (gsmSCF) through a Customized Application for Mobile network Enhanced Logic (CAMEL) Application Part (CAP) interface; or the GMSC in the cdma2000 CS domain interacts with the RPDP functioning as a Wireless intelligent Network (WIN) Service Control Function (SCF) through an American National Standards Institute-41 Mobile Application Protocol (ANSI-41 MAP); or a local exchanger in the PSTN interacts with the RPDP functioning as a fixed Intelligent Network (IN) SCF through an Intelligent Network Application Protocol (INAP); or the S-CSCF in the IMS interacts with the RPDP functioning as an AS through an IMS Service Control interface (ISC). Thus, the query of the routing decision and the routing control according to the routing decision may be implemented.
In the second mode, the routing control entity in the CS/IMS queries the RPDP for the routing decision through the non-call-control protocol based interface. For example, the RPDP which functions as a Signaling Transfer Point (STP) intercepts a routing information query message from the GMSC to the HLR in the GSM, WCDMA CS domain or cdma2000 CS domain; or the HLR in the GSM, WCDMA CS domain or cdma2000 CS domain queries, upon the receipt of the routing information query message from the GMSC, the RPDP through a new interface; or the HSS in the IMS queries, upon the receipt of the routing information query message from the I-CSCF, the RPDP through another new interface, so as to implement the query of the routing decision and the routing control according to the routing decision.
However, in the above two modes, the routing-decision-making related information of the user in the CS/IMS for making the routing decision is always obtained by interacting with the HLR/HSS. For example, the RPDP queries, the HLR/HSS for the routing-decision-making related information when making the routing decision, or locally stores the routing-decision-making related information and the HLR/HSS updates the routing-decision-making related information stored in the RPDP when the routing-decision-making related information changes. The HLR/HSS has no knowledge about which domain is used by an existing call. In other words, the HLR/HSS has no knowledge of call status(es) of the user in any one or both of the CS domain and the IMS. Therefore, the existing solution does not consider the call status(es) of the user in any one or both of the CS domain and the IMS. In other words, under the scenario that the user may register in both the CS domain and the IMS, the existing solution does not consider how to select the domain to deliver an incoming call to avoid the problem that two calls are delivered via two domains while the user can only accept one of the calls.
In practical applications, a UE usually has one audio I/O channel (voice channel) and the user usually can only answer one call at one time. Even when the UE is capable of accessing both the CS domain and the IMS at the same time and establishing calls in the CS domain and the IMS, it is impossible to engage in two voice calls respectively in the CS domain and the IMS at the same time. Therefore when routing an incoming call, it is necessary to avoid an abnormal condition that two calls are delivered to the user via the CS domain and the IMS respectively while the user can only answer one of them.
In the related art, there are services capable of handling multiple calls or a subsequent call in one domain. For example, in the CS domain, several supplementary services are defined to handle the subsequent call during an existing call, including call waiting, call holding, multi-party service, call forwarding on subscriber busy, etc. Thus, an incoming call may be handled when there exist an existing call. In the IMS, although no such service is defined in detail as in the CS domain, there are similar services to handle the subsequent call.
Therefore, in the case that the two domains are capable of providing voice services to the user at the same time, it is necessary to avoid the problem that a call is delivered to the user via a domain other than the domain in which the user has an existing call, i.e., it is necessary to deliver the subsequent call to the domain in which the user has an existing call. Thus, the mechanism in the related art, e.g., the supplementary services in the CS domain, may be employed to handle the subsequent call.
The GSM, WCDMA CS domain and cdma2000 CS domain have similar network architectures, and the intelligent networks of the PSTN, GSM, WCDMA and cdma2000 system have basically the same architecture. Moreover, the IMS defined by different organizations have similar architectures, i.e., the IMS accessed via various fixed/mobile IPCAN have similar architectures. Therefore the problem and requirement of the domain selection in the related art are the same in different systems.